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CHICAGO - Impoverished children struggle under an invisible weight that often crushes their intellectual potential, according to a growing body of research that gives new insight into how environment shapes the developing brain.
A recent University of Virginia study shows that poverty can erase a number of points from a child's IQ score.
Another recent study found that inadequate nutrition early in life combined with a lack of schooling can wipe out much of a child's potential for learning. Good food and schooling can lead to substantial intellectual gains in adulthood.
Both studies support a growing conviction among scientists that genes are not immutable commandments dictating a child's mental potential. Instead, gene function is highly dependent on environmental experiences, underperforming in adverse circumstances and achieving their full potential in favorable ones.
"We're finding that early life shapes the expression of genes," said Reynaldo Martorell of Emory University, whose study of nutritional supplements and early education appears in the current issue of "Pediatrics," a journal of the American Academy of Pediatrics. "You're born with a range of possibilities and your early environment can shape how you develop."
The findings of the IQ and environment study are sure to add fuel to the long-standing and often bitter debate over which is more important for mental development, genes or environment.
"There's a furious nature-nurture debate on this," said neurologist Paul Thompson of the University of California, Los Angeles. "The genetics people say IQ is a basic mental capacity that we largely inherit, like our height or fingerprints. So it's very difficult to change your IQ.
"But this flies in the face of the wealth of new neuroscience studies showing how changeable the brain is throughout life," Thompson said. "This paper resolves that paradox. It is saying that your environment can have a big impact on your IQ."
The findings are likely to be used in the debate over public policy, especially the ongoing fight by the Bush administration to give states control over the federal Head Start program.
"By showing that the environment in impoverished families makes a big difference, that's of course exactly the environment that special programs like Head Start are targeted at," said the study's lead author, psychologist Eric Turkheimer of the University of Virginia.
The Virginia study is the first to compare large numbers of twins from rich and poor families. It appears in the current issue of "Psychological Science," a publication of the American Psychological Society.
Its main finding: Poverty, lack of educational opportunities and other deleterious environmental factors account for 80 percent of the decline in IQ scores of very impoverished twins, scores that can be 40 points lower than the IQ scores of twins from rich families who have maximum environmental advantages.
"These results, if they are replicated, will prove to be a landmark in the study of intelligence," said psychologist Robert Sternberg, director of Yale University's Center for the Psychology of Abilities, Competencies and Expertise. "It suggests that intelligence and its heritability cannot be understood outside their environmental context."
Previous twin studies, which did not include poor and rich children, served as the foundation for the "Bell Curve" and other writings contending that if the environment children are raised in doesn't make any difference for their IQ, efforts to improve the environment may have no effect on raising intellectual achievement.
Twins are used to pull out differences between genes and environment because identical twins have the same set of genes and tend to have similar traits such, as IQ. Fraternal twins share 50 percent of the same genes, so their traits vary more broadly.
Turkheimer found that IQ scores among pairs of identical twins from richer families were basically the same and that fraternal twins from richer families averaged a 15-point difference between members of the same set.
But among the poorest twins, Turkheimer did not find that pattern. Instead of finding a difference in the IQ levels of the fraternal twins he found little or none, indicating that their environment was overwhelming the ability of their genes to produce different intelligence abilities, Turkheimer said.
"That not only makes sense, but it resolves some contradictory studies," said Thompson, who was not involved in the Virginia study. "If you are rich, the chances are there is little you can do to affect your IQ, as you have already optimized most of the factors that affect it," like education, nutrition, overall health and so on.
Children in impoverished families, on the other hand, often lack adequate nutrition, talking, reading and other forms of normal mental stimulation that genes need to build the brain circuitry for intelligence, he said.
Impoverished twins in the Virginia study lived in families whose average annual income was less than $12,000, half the fathers were absent, 1 of 4 mothers had less than a ninth 9th grade education, and the children lived in homes with two people to a room.
In the Emory study, Martorell examined Guatemalan women who were given nutritional supplements in the first two years of life and schooling through the primary grades. Undernutrition and malnutrition are common in Guatemalan children.
Re-examining the women in their 20s, Martorell found that those who had received the supplements and schooling had academic achievement scores 33 percent higher than women who neither received supplements nor completed primary school.
Primary education alone improved the achievement scores of women not given nutrition supplements by about 20 percent, but the improvement increased by another 50 percent among those receiving supplements as well as education, Martorell said. "You're going to get quite a return on your investment if you foster education," he said. "But if you also improve nutrition in early childhood, your return will be magnified."
(c) 2003, Chicago Tribune. Distributed by Knight Ridder/Tribune News Service.